B1: Scroll restoration race on async Mermaid render

[jverhoeks]

Source: codebase-review.md — Bug B1

File: tabs.ts:265–286

repaint fires async renderers (Mermaid) without await, so scrollTop is restored before async DOM mutations complete, causing a visual jump when viewing documents with diagrams.

Fix: await all async renderers before restoring scroll position.

[jverhoeks]

Already fixed. repaint in tabs.ts:439 + 444-449 uses a double-settle pattern — initial settle after sync render, then re-settle after async Mermaid/Math promises resolve. See tabs.ts:437-449.